and senator roger wicker. the move comes just days after the betters were intercepted in mail-sorting facilities. tracie potts is live with the details. >> reporter: authorities after an exhaustive investigation traced the letters to paul kevin curtis of tupelo, mississippi. he was arrested at his home in mississippi, as authorities try to figure out what the motive was here. three letters that tested positive for potentially dangerous ricin. the one sent to senator wicker never made it to capitol hill. it was intercepted. one sent to president obama was intercepted offsite. all of them postmarked april 8th. and all postmarked for memphis. what gave it away was the common signature. i am kevin curtis and i approve this message, at the end of the letters. the test on the first letter to wicker, had proved inconclusive. and the second one, as well. they're trying to figure out how potent this ricin was. and while it initially tested positive, the further tests by the fbi have been inconclusive. they ordered more